Distribution of fibrillar centers and silver-stained components in the nucleolus of human Sertoli cells

The nucleolus of the human Sertoli cell consistently showed three distinct, spontaneously segregated parts: 1. one or two large, silver-positive fibrillar centers; 2. strands of dense fibrillar component continuous with the dense cords surrounding the fibrillar center. These components were also silver-positive; 3. a granular, silver-negative mass. These observations show that in the human Sertoli cell the number of fibrillar centers is far lower than the diploid number of NORs. They also suggest that the fibrillar center might contain several NORs in this cell type.     

Three-dimensional analysis of fibrillar centers and associated chromatin in the nucleolus of human oocytes in primordial follicles

The intranucleolar localization of fibrillar centers and their relationships with nucleolus-associated chromatin were determined in stereopairs of human oocyte nucleoli obtained by computer reconstruction of serial sections. This study showed that there was no numerical relationship between the number of fibrillar centers and the number of chromosomal NORs. The three-dimensional reconstruction demonstrated that the majority of fibrillar centers was directly connected with the nucleolus-associated chromatin.     

Changes in nucleolar structure,number and size in cellular activation and inactivation

In a cytophysiological study it was investigated whether in juvenile trout gonadal steroids stimulate the gonadotropic (GTH)-cells directly or indirectly via the brain. Pituitaries of donor animals were transplanted into the caudal musculature of testosterone-treated and non-testosterone-treated host fish. Testosterone treatment caused an increase in GTH-content in the in situ pituitaries and in the grafts. Accordingly, the gonadotrops displayed ultrastructural changes such as the appearance of well-developed Golgi systems and large globules. The stimulation of the morphological development of gonadotrops and of synthesis and storage of GTH in the allografted pituitaries indicates that testosterone affects the GTH-cells directly. In untreated juvenile trout the gonadotropin content of the pituitary and the gonadotropin concentration in the plasma vary with the time of year. This variation and the role of testosterone and gonadotropin-releasing hormone on the release of GTH are discussed.     

Correlation of the nucleolar organizer and the fibrillar center of the nucleolus

The review is dedicated to the question, to what extent it is possible to speak about the correspondence of the fibrillar center (FC) of the nucleolus to the nucleolar organizer region (NOR) of the metaphase chromosome. The analysis of the literature on the problem provides grounds for the affirmation that the chromatin-containing elements of the FC and of the fibrillar component of the nucleolus correspond to the NOR. At the same time, the number of facts evidence in favour of the hypothesis that the FC serves as a kind of "depot" for nucleolar proteins. The latter makes it possible to consider the FC to be polyfunctional.     

Changes in erythropoiesis during the course of polycythaemia vera.

Using 58Fe, 51Cr and cytological parameters, the authors have examined erythropoiesis in 44 polycythaemia vera patients diagnosed as such on the basis of the usual parameters (exept for determination of the erythropoietin level). In the patients divided into four types the following characteristica were observed. In type I, increased erythropoiesis is evident by accelerated plasma iron clearance, greater PIT and EIT as well as enhanced iron utilization and production indices. In type II, in addition to the former signs of increased erythropoiesis moderately shortened red cell life-span and hyposideraemia characteristic of splenic sequestration and resulting from bleeding and blood letting seem to be accompanied by microcytosis. There is a metaplastic erythropoiesis in type III, bone marrow activity decreases, but the increased erythropoiesis is indicated by several parameters already observed earlier. At the time the iron utilization indicative of effective erythropoiesis is decreased, thus ineffective erythropoiesis and considerably shortened red cell life-span are responsible for the enhanced iron turnover. This is also shown by the regression calculations. In type IV effective erythropoiesis was considerably decreased in the patients with severe anaemia. Sings which are indicative of metaplastic erythropoiesis are absent. In one of the patients the morphological changes characteristic of dyserythropoiesis were found. Although all our patients were given treatment. We believe that these alterations in the character of erythropoiesis are not likely to be the consequences of therapy.     

Studies on chromatin organization in a nucleolus without fibrillar centres

In embryonic cell-line derivative KCo of Drosophila melanogaster, the nucleolus, like most nucleoli, contains a small proportion of ribosomal DNA (1-2% of the total nucleolar DNA). The ribosomal DNA is virtually the only active gene set in the nucleolus and is found among long stretches of inactive supercoiled heterochromatic segments. We have demonstrated by use of a Feulgen-like ammine-osmium staining procedure that, depending on the state of growth, more or less fibres of decondensed DNA emanating from the intra-nucleolar chromatin (which is in continuity with the nucleolus-associated chromatin) ramify and unravel within the central nucleolar core to be transcribed. The nucleolus expands or contracts with the variation of activity and could belong to a supramolecular matricial structure such as is shown after extraction of the nuclei. After a long period of exposure to high doses of actinomycin D, the central nucleolar core became an homogeneous fibrous structure that could be interpreted as an aggregate of protein skeletal elements. The mechanism of repression and derepression of the nucleolar chromatin could thus be explained by a mechanism involving in part a sub-nucleolar structure. We propose a schematic organization of the nucleolar chromatin in KCo cells of Drosophila and discuss it in relation with other nucleolar organizations.     

Nucleolar fibrillar centers in mouse spermatid nucleoli

The nucleoli of young spermatids of mice are described. They exhibit a very special shape resembling a "padlock" in which three different areas can be distinguished: (a) a compact zone corresponding to the fibrillar component, (b) the granular component and (c) a fibrillar center of low density. Fibrillar and granular components usually appear segregated. This nucleolus has been reconstructed based on serial sectioning. When the silver impregnation technique is employed, both fibrillar and granular components show a positive reaction, although the fibrillar center is free of granules. The morphology of the fibrillar center seems to be similar to that reported in other cells. The possibility that these fibrillar centers correspond to the nucleolar organizer is discussed.     

Partial inactivation of wheat nucleolus organisers by the nucleolus organiser chromosomes from Aegilops umbellulata

Two pairs of chromosomes (1U and 5U) in Aegilops umbellulata possess ribosomal RNA genes. This has been proven by studying wheat plants into which 1U and 5U chromosomes have been introduced separately. These plants have more ribosomal RNA genes than the recipient wheat plants and additional clusters of rDNA when examined by in situ hybridisation. The repeating rDNA unit in Aegilops umbellulata is longer than most of the units in the wheat variety Chinese Spring, the additional DNA probably being in the non-transcribed spacer. This was determined from restriction endonuclease maps of rDNA. In Chinese Spring plants possessing 1U or 5U chromosomes, the largest nucleoli are formed on 1U or 5U chromosomes and the wheat nucleolus organisers form micronucleoli. This is not because the nucleolus organisers on chromosomes 1U and 5U have many more rRNA genes than wheat nucleolus organisers. It is suggested that the Aegilops umbellulata nucleolus organisers are dominant over those of wheat because they compete more effectively for some limiting factor. — The partial inactivation of the wheat nucleolus organisers by chromosomes 1U or 5U does not result in a reduced total nucleolus volume in root tip or pollen mother cells, because of the compensation by the nucleolus organisers of chromosomes 1U or 5U. The amount of RNA in seedlings is not markedly affected by the partial inactivation of the wheat nucleolus organisers.     

Changes in membrane structure and function during chick embryonic erythropoiesis.

We found considerable differences in the pattern of membrane proteins as well as in the relative amounts of individual components in isolated chick red blood cell membranes during the course of embryonic development. Of special interest in the increase in the relative amounts of two major polypeptides, band 3 and 3.1 (MW 100,000 daltons) with increasing age of the cells. With respect to functional studies, we found that the magnitude of sulfate influx decreases with increasing age of the embryo. Furthermore, the activity of ouabain-sensitive ATPase increases with increasing age (2.5-day embryo to adult). In addition, both the basal and the fluoride-stimulated adenylate cyclase activities decrease as the embryo age increases, whereas the enzyme sensitivity to epinephrine increases with increasing age of the embryo.     

Changes in the inactivation of rat Kv1.4 K(+) channels induced by varying the number of inactivation particles

N-type inactivation of rat Kv1.4 channels with one, two, or four inactivation balls was investigated using homogeneous populations of channels expressed in Xenopus oocytes. Tandem dimeric and tetrameric constructs of Kv1.4 were made. Channels encoded by tandem cDNAs Kv1. 4-Kv1.4Delta1-145 and Kv1.4-[Kv1.4Delta1-145](3) have two or only one tethered inactivation ball, respectively, whereas Kv1.4 itself encodes channels having four inactivation balls. The time constants for inactivation of macroscopic currents were increased significantly as the number of inactivation balls was decreased, whereas the time constants for recovery from inactivation were not modified. The ratios of the rate constants of inactivation (k(inact)) of Kv1.4-Kv1.4Delta1-145 and Kv1.4-[Kv1.4Delta1-145](3) channels to that of the Kv1.4 channel were 0.65 and 0.4, respectively, whereas the ratios of the rate constant of recovery (k(rec)) of these channels to that of Kv1.4 were almost unity. The rate constants k(inact) for channels having two and four inactivation balls are smaller than those that would be expected if inactivation balls on each channel are independent, suggesting some interaction occurs between inactivation balls. Furthermore, noninactivating current became apparent as the number of inactivation balls on a channel was decreased.     

Does the synthesis of ribosomal RNA take place-within nucleolar fibrillar centers or dense fibrillar components?

By means of immunocytochemistry performed on cryosections of cultured cells, RNA polymerase I was localized mainly to nucleolar fibrillar centers. The labelling of nucleolar dense fibrillar components was low and depended on the cell type. In contrast, DNA topoisomerase I and RNP complexes containing U3 snRNA were enriched in dense fibrillar components, their occurrence in fibrillar centers being usually much less.     

Changes in nucleus, nucleolus and cell size accompanying somatic embryogenesis of Theobroma cacao L. II. Relation between basic protein content and size of nucleus, nucleolus and cell

Embryo formation from callus of Theobroma cacao L. was associated with the changes in relationship between nuclear, nucleolar and cell sizes and the content of basic proteins (FG-FCF-stained). Together with the increase in nuclear size of callus and proembryo cells the increase in the amount of nuclear basic proteins was found. In the callus cells the increase in nucleolar protein content exceeded that in nucleolus size, which led to the rise in basic protein concentration in the nucleolus. However, in the early stage of embryogenesis the increase in protein content was not so marked as that in callus, which indicated that embryogenesis involved a decrease in concentration of nucleolar basic proteins. Differences between callus and proembryo cells were also observed in the concentration of cytoplasmic proteins. The increase in size of callus cells was the same as the increasing amount of cytoplasmic proteins. In proembryos a significant increase in cell size was accompanied by only slight changes in cytoplasmic proteins. The stimulation of embryogenesis by 2,4-D resulted in an increase of nuclear concentration of basic proteins in proembryos. The intensification of embryogenesis involved the decrease of the concentration of nucleolar proteins together with the increase in concentration of basic cytoplasmic proteins.     

Changes in brain size during the menstrual cycle

Background

There is increasing evidence for hormone-dependent modification of function and behavior during the menstrual cycle, but little is known about associated short-term structural alterations of the brain. Preliminary studies suggest that a hormone-dependent decline in brain volume occurs in postmenopausal, or women receiving antiestrogens, long term. Advances in serial MR-volumetry have allowed for the accurate detection of small volume changes of the brain. Recently, activity-induced short-term structural plasticity of the brain was demonstrated, challenging the view that the brain is as rigid as formerly believed.

Methodology/Principal Findings

We used MR-volumetry to investigate short-term brain volume changes across the menstrual cycle in women or a parallel 4 week period in men, respectively. We found a significant grey matter volume peak and CSF loss at the time of ovulation in females. This volume peak did not correlate with estradiol or progesterone hormone levels. Men did not show any significant brain volume alterations.

Conclusions/Significance

These data give evidence of short-term hormone-dependent structural brain changes during the menstrual cycle, which need to be correlated with functional states and have to be considered in structure-associated functional brain research.